<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>速率控制</title>
  <style>
    div{
      width: 50px;
      height: 100vh;
      background-color: cyan;
      
    }
    main{
      width: 100%;
      height: 100%;
      background-color: white;
      animation-name: descrease;
      animation-duration: 2s;
      animation-direction: reverse;
    }
    @keyframes descrease{
      from{}
      to{
        height: 0;
        /* margin-top: 100%; */
        animation-timing-function: ease-in-out;
      }
    }
  </style>
</head>
<body>
  <div>
    <main></main>
  </div>
</body>
</html>